There has been increasing interest in the use of flexible, collapsible containers for handling semi-bulk quantities of particulate, granular and other flowable materials such as chemicals, minerals, fertilizers, foodstuffs, grains, and agricultural products. The advantages of such receptacles include relatively low weight, reduced cost, better versatility, and low return freight costs in the case of reusable receptacles.
Fabrics are often used in the construction of such containers for strength, flexibility and durability. Traditionally, fabrics have been constructed of natural fibers; however, in recent years synthetic fibers manufactured from polypropylene or other plastics have come into extensive use because they are generally stronger and more durable than fabrics made of natural fiber.
The electrical characteristics of fabrics make their use undesirable in some circumstances. For example, many granular and liquid materials develop a static-electric charge through friction as they are poured into, discharged from or vibrated within a receptacle. Because fabrics are not electrically conductive, discharge of static-electricity from such materials contained by fabric receptacles is difficult, if not impossible, posing the danger of explosion or fire caused by an electrical spark.
Previously, to reduce static electricity problems, a layer of metalized fabric or a metallic laminate such as an aluminum or other electrically conductive metal foil has been secured to the fabric and the fabric was used to construct a receptacle and a discharge spout with the foil laminate or metalized layer comprising the interior surface of the receptacle and the discharge spout. The metal layers were then grounded to eliminate static electricity.
Foil laminates and metalized fabrics are, however, susceptible to abrasion, tearing and separation from the underlying fabric, particularly along the edges of the foil laminate due to contact with the contents of the receptacle as the receptacle is filled, emptied or transported. Such abrasion quickly reduces the effectiveness of the foil layer as a grounding surface and often results in unwanted contamination of the contents of the bag with foil particles or flakes.